Dye-sensitized solar cell with hybrid nanostructures and method for fabricating working electrodes thereof

ABSTRACT

A dye-sensitized solar cell with hybrid nanostructures comprises a negative-polarity conductive substrate, a metal oxide layer, a positive-polarity conductive substrate and an electrolyte. The metal oxide layer has a plurality of nanoparticles and a plurality of nanotubes. The metal oxide layer and the electrolyte are arranged between the negative-polarity conductive substrate and the positive-polarity conductive substrate. The nanoparticles increase contact area with dye and thus enhance power generation efficiency. The nanotubes increase carrier mobility and thus effectively transfer electricity to electrodes. The solar cell integrates the advantages of nanoparticles and nanotubes and offsets the disadvantages thereof to effectively enhance the photovoltaic conversion efficiency of dye-sensitized solar cells.

FIELD OF THE INVENTION

The present invention relates to a solar cell, particularly to adye-sensitized solar cell with hybrid nanostructures.

BACKGROUND OF THE INVENTION

In DSSC (Dye-Sensitized Solar Cell), dye molecules are chemicallyabsorbed by metal oxide semiconductor nanoparticles; then, thenanoparticles are spread on the cathode to function as a photosensitivelayer; an electrolyte is interposed between the photosensitive layer andthe anode to assist in electric conduction. DSSC has the followingadvantages:

-   1. The photosensitive particles have an effective light absorption    area 100 times greater than the surface area of the electrode.    Therefore, DSSC has very high light absorption efficiency, using a    very small amount of material.-   2. The photosensitive particles are fabricated via merely soaking    the semiconductor particles in a dye solution and drying the    particles with an inert gas. Therefore, DSSC has a simple and    inexpensive fabrication process.-   3. The dye of DSSC has a wide absorption spectrum in the range of    visible light. Therefore, a single type of DSSC elements can harness    a wide spectrum of solar light.-   4. DSSC is semitransparent and suitable to be a construction    material, especially a window material. For example, DSSC may be    used as glass curtain walls of high-rise buildings to provide    functions of sunlight sheltering, thermal insulation and power    generation. Therefore, a building may have efficacies of power    saving and power generation via using DSSC.

Generally, a solar cell is expected to have low cost, low fabricationcomplexity, and high photovoltaic conversion efficiency. DSSC indeed hasthe characteristics of low cost and low fabrication complexity. However,the photovoltaic conversion efficiency thereof still needs improving. AR.O.C patent publication No. 201001724 disclosed a “Dye Sensitized SolarCell Having a Double-Layer Nanotube Structure and Manufacture MethodThereof”. The nanotube structures can increase the electric conductionefficiency of DSSC. However, nanotubes have less area to absorb dye thannanoparticles. Thus is decreased the photovoltaic conversion efficiencyof the prior-art DSSC.

SUMMARY OF THE INVENTION

The primary objective of the present invention is to enhance thephotovoltaic conversion efficiency of dye-sensitized solar cells.

To achieve the abovementioned objective, the present invention providesa dye-sensitized solar cell with hybrid nanostructures, which comprisesa negative-polarity conductive substrate, a positive-polarity conductivesubstrate, a metal oxide layer and an electrolyte. The metal oxide layeris arranged between the negative-polarity conductive substrate and thepositive-polarity conductive substrate. The metal oxide layer has aplurality of nanoparticles and a plurality of nanotubes. Thenanoparticles and nanotubes are arranged alternately. The metal oxidelayer is adhered to the negative-polarity conductive substrate. Theelectrolyte is arranged between the negative-polarity conductivesubstrate and the positive-polarity conductive substrate to implementredox reactions of the metal oxide layer.

The present invention also provides a method for fabricating adye-sensitized solar cell with hybrid nanostructures, which comprisessteps: fabricating nanotubes with an anodizing method; breaking off thenanotubes via a vibration method; mixing the nanotubes withnanoparticles to obtain a metal oxide mixture; and spreading the metaloxide mixture on a conductive substrate to obtain a working electrode ofa dye-sensitized solar cell.

The nanoparticles can effectively increase the contact area between themetal oxide mixture and dye and thus enhance the photovoltaic conversionefficiency of DSSC. The nanotubes can increase the carrier mobility toeffectively transfer electric energy to the electrodes. The presentinvention combines the advantages of nanoparticles and nanotubes andoffset the disadvantages thereof to obtain greater dye absorption areaand higher carrier mobility and improve the photovoltaic conversionefficiency of a dye-sensitized solar cell.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically showing the structure of a workingelectrode of a dye-sensitized solar cell according to one embodiment ofthe present invention;

FIG. 2 is a diagram schematically showing the structure of adye-sensitized solar cell according to one embodiment of the presentinvention; and

FIG. 3 is a diagram schematically showing the structure of adye-sensitized solar cell according to another embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The technical contents of the present invention are described in detailin cooperation with the drawings below.

Refer to FIG. 1 and FIG. 2 respectively diagrams schematically showingstructures of a working electrode and a dye-sensitized solar cellaccording to one embodiment of the present invention. The presentinvention provides a dye-sensitized solar cell with hybridnanostructures, which comprises a negative-polarity conductive substrate10, a positive-polarity conductive substrate 20, a metal oxide layer 30and an electrolyte 40. The metal oxide layer 30 is arranged between thenegative-polarity conductive substrate 10 and the positive-polarityconductive substrate 20. The metal oxide layer 30 has a plurality ofnanoparticles 32 and a plurality of nanotubes 31. The nanoparticles 32and nanotubes 31 are arranged alternately. The metal oxide layer 30 isadhered to the negative-polarity conductive substrate 10. Theelectrolyte 40 is arranged between the negative-polarity conductivesubstrate 10 and the positive-polarity conductive substrate 20 toimplement redox reactions of the metal oxide layer 30. In the embodimentshown in FIG. 2, the metal oxide layer 30 is arranged on one side of thenegative-polarity conductive substrate 10; the electrolyte 40 isarranged between the metal oxide layer 30 and the positive-polarityconductive substrate 20. A catalytic layer 50 is arranged between theelectrolyte 40 and the positive-polarity conductive substrate 20. Thecatalytic layer 50 is made of platinum in this embodiment. The processof absorbing light and generating electricity is the basic principle ofDSSC and will not repeat here.

The nanotubes 31 are grown with an anodizing method. In this embodiment,the metal oxide layer 30 is made of titanium dioxide. The nanotubes 31are grown from titanium with an anodizing method. Then the nanotubes 31are broken off with a vibration method and collected. The nanotubes 31and nanoparticles 32 are arranged alternately. The negative-polarityconductive substrate 10 and the positive-polarity conductive substrate20 are made of ITO (Indium Tin Oxide). A dye sensitizer adheres to thesurface of the nanoparticles 32 and nanotubes 31.

Refer to FIG. 3 a diagram schematically showing the structure of adye-sensitized solar cell according to another embodiment of the presentinvention. In this embodiment, the electrolyte 40 is arranged on twosides of the metal oxide layer 30. Such a structure can also implementthe redox reaction of DSSC.

The present invention also provides a method for fabricating adye-sensitized solar cell with hybrid nanostructures, which comprisessteps:

S1: fabricating nanotubes 31, wherein an anodizing method is used togrow a plurality of nanotubes 31 from a metal substrate; in oneembodiment, the metal substrate is made of titanium (Ti);

S2: fabricating a metal oxide mixture, wherein the nanotubes 31 arebroken off by vibration and then mixed with nanoparticles 32 to form ametal oxide mixture;

S3: fabricating an electrode, wherein the metal oxide mixture is spreadon a conductive substrate to form a negative-polarity conductivesubstrate 10 functioning as a working electrode; in one embodiment, themetal oxide mixture is spread on the conductive substrate with aspin-coating method.

The abovementioned steps can only fabricate the negative-polarityconductive substrate 10. To complete a solar cell further needs thefollowing steps:

S4: dye adhering, wherein the negative-polarity conductive substrate 10is soaked in a dye sensitizer to make dye adhere to the surface of thenanoparticles 32 and nanotubes 31;

S5: joining the negative-polarity conductive substrate 10 with thepositive-polarity conductive substrate 20 to complete a solar cell,wherein the positive-polarity conductive substrate 20 is adhered to oneside of the negative-polarity conductive substrate 10 having the metaloxide mixture by an electrolyte 40.

As the nanoparticles 32 have larger contact area for adhering dye, theycan effectively convert light energy into electric energy. However,there are only point contacts among particles. Therefore, thenanoparticles 32 have poor electric conductivity. Although the nanotubes31 have smaller surface area, they can effectively conduct electricityto the conductive substrates via the tube structure thereof. Theelectricity generated by the nanoparticles 32 is transmitted to thenanotubes 31 via the contact points between the nanoparticles 32 and thenanotubes 31, and the nanotubes 31 collect and send out electricity. Asdye also adheres to the surface of the nanotubes 31, the nanotubes 31generate electricity too.

In summary, the nanoparticles 32 increase the contact area between dyeand the metal oxide mixture and thus enhance the photovoltaic conversionefficiency of the solar cell. The nanotubes 31 increase carrier mobilityand thus effectively transfer electricity to electrodes. The presentinvention integrates the advantages of nanoparticles 32 and nanotubes 31and offsets the disadvantages thereof to achieve large dye-adhering areaand high carrier mobility so as to enhance the photovoltaic conversionefficiency of DSSC.

1. A dye-sensitized solar cell with hybrid nanostructures, comprising anegative-polarity conductive substrate; a positive-polarity conductivesubstrate; a metal oxide layer arranged between the negative-polarityconductive substrate and the positive-polarity conductive substrate, andhaving a plurality of nanoparticles and a plurality of nanotubes; and anelectrolyte arranged between the negative-polarity conductive substrateand the positive-polarity conductive substrate.
 2. The dye-sensitizedsolar cell according to claim 1, wherein the nanotubes are grown with ananodizing method.
 3. The dye-sensitized solar cell according to claim 2,wherein the metal oxide layer is made of titanium dioxide, and whereinthe nanotubes are grown from titanium and then broken off from titaniumdioxide via vibration, and wherein the nanotubes and the nanoparticlesare arranged alternately.
 4. The dye-sensitized solar cell according toclaim 1, wherein a dye sensitizer adheres to surface of thenanoparticles and nanotubes.
 5. The dye-sensitized solar cell accordingto claim 1, wherein a catalytic layer is arranged between thepositive-polarity conductive substrate and the metal oxide layer.
 6. Thedye-sensitized solar cell according to claim 5, wherein the catalyticlayer is made of platinum.
 7. A method for fabricating workingelectrodes of a dye-sensitized solar cell, comprising steps: growing aplurality of nanotubes from a metal substrate with an anodizing method;breaking off the nanotubes via vibration, and mixing the nanotubes withnanoparticles to form a metal oxide mixture; and spreading the metaloxide mixture on a conductive substrate.
 8. The method for fabricatingworking electrodes of a dye-sensitized solar cell according to claim 7,wherein the metal oxide mixture is spread on the conductive substratewith a spin-coating method.
 9. The method for fabricating workingelectrodes of a dye-sensitized solar cell according to claim 7 furthercomprising a step of soaking the conductive substrate in a dyesensitizer.
 10. The method for fabricating working electrodes of adye-sensitized solar cell according to claim 7, wherein the conductivesubstrate coated with the metal oxide mixture functions as anegative-polarity conductive substrate, and further comprising a step ofintegrating the negative-polarity conductive substrate and apositive-polarity conductive substrate to form a solar cell.